Visible-light assisted one-pot preparation of aryl glyoxals from acetoarylones via in-situ arylacyl bromides formation: Selenium-free approach to acetoarylones oxidation

Article abstract of DOI:10.1016/j.tetlet.2017.01.013

A novel visible-light (blue LEDs: hν?=?425?±?15?nm) photocatalyzed one-pot method for the synthesis of electronically diverse aryl glyoxals in good to excellent yields from acetoarylones and green regents such as air, vitamin C and dioxane dibromide has been described. In addition, an application of the current methodology has been demonstrated for the oxidation of monoamine oxidase-B inhibitors, i.e., 1-(4-((4-fluorobenzyl)oxy)phenyl)ethanone and 1-(3-((4-chlorobenzyl)oxy)phenyl)ethanone. This finding may serves as a valuable alternative to the traditional acetoarylones oxidation reactions conducted using selenium dioxide a harmful and unselective reagent known to simultaneously oxidize allylic, benzylic, [sbnd]CH₃and so on.

Full text of DOI:10.1016/j.tetlet.2017.01.013

Accepted Manuscript
Visible-light assisted one-pot preparation of aryl glyoxals from acetoarylones
via in-situ arylacyl bromides formation: Selenium-free approach to acetoary-
lones oxidation
Palani Natarajan, Manjeet, Naveen Kumar, Sapna Devi, Kalyani Mer
PII:
S0040-4039(17)30023-0
DOI:
http://dx.doi.org/10.1016/j.tetlet.2017.01.013
TETL 48516
Reference:
Tetrahedron Letters
To appear in:
Received Date:
Revised Date:
Accepted Date:
16 December 2016
31 December 2016
3 January 2017
Please cite this article as: Natarajan, P., Manjeet, Kumar, N., Devi, S., Mer, K., Visible-light assisted one-pot
preparation of aryl glyoxals from acetoarylones via in-situ arylacyl bromides formation: Selenium-free approach to
acetoarylones oxidation, Tetrahedron Letters (2017), doi: http://dx.doi.org/10.1016/j.tetlet.2017.01.013
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers
we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and
review of the resulting proof before it is published in its final form. Please note that during the production process
errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Graphical Abstract
To create your abstract, type over the instructions in the template box below.
Fonts or abstract dimensions should not be changed or altered.
Visible-light assisted one-pot preparation of aryl glyoxalLsefarvoemthaisceatroeaarbyllaonnkesfovriaabisnt-rsaicttuinafroy.lacyl
bromides formation: Selenium-free approach to acetoarylones oxidation
Palani Natarajan*, Manjeet, Naveen Kumar, Sapna Devi and Kalyani Mer

1
Tetrahedron Letters
Visible-light assisted one-pot preparation of aryl glyoxals from acetoarylones via
in-situ arylacyl bromides formation: Selenium-free approach to acetoarylones
oxidation
Palani Natarajan*, Manjeet, Naveen Kumar, Sapna Devi and Kalyani Mer
Department of Chemistry & Centre for Advanced Studies in Chemistry, Panjab University, Chandigarh - 160014, India
pnataraj@pu.ac.in
ARTICLE INFO
ABSTRACT
Article history:
Received
Received in revised form
Accepted
A novel visible-light (blue LEDs: h = 42515 nm) photocatalyzed one-pot method for the
synthesis of electronically diverse aryl glyoxals in good to excellent yields from acetoarylones
and green regents such as air, vitamin C and dioxane dibromide has been described. In addition,
an application of the current methodology has been demonstrated for the oxidation of
monoamine oxidase-B inhibitors, i.e., 1-(4-((4-fluorobenzyl)oxy)phenyl)ethanone and 1-(3-((4-
chlorobenzyl)oxy)phenyl)ethanone. This finding may serves as a valuable alternative to the
traditional acetoarylones oxidation reactions conducted using selenium dioxide a harmful and
unselective reagent known to simultaneously oxidize allylic, benzylic, -CH3 and so on.
Available online
Keywords:
Keyword_1 aryl glyoxals
Keyword_2 one-pot synthesis
Keyword_3 photoredox catalysis
Keyword_4 visible light
Keyword_5 oxidation reaction
2009 Elsevier Ltd. All rights reserved.
1. Introduction
reactions. Using a visible light photoredox catalysis13 and 9,10-
dihydro-10-methylacridine as both electron and proton sources,
The aryl glyoxals1 are very important dielectrophilic
precursors that have been used in organic synthesis for the
construction of natural products and heterocyclic compounds
including hydantoins, imidazoles, oxadiazoles and thiopheno-
diones2. Moreover, they have been used in medicinal chemistry
as drugs to modify amino acids and arginines3. The aryl glyoxals
were first successfully prepared by thermal decomposition of the
sulfite derivative of the oxime4, i.e., C6H5C(O)CH(NOSO2H).
However, this method is seldom used due to poor atom economy
and difficulties associated with the product purification from
sulfamic acid a byproduct. In last 60 years, aryl glyoxals in bulk
have been prepared from acetoarylones by oxidation using
selenium dioxide (SeO2) in aqueous solutions5,6. Despite the fact
that oxidation performed in aqueous medium, but it suffers with
several drawbacks such as requires more than stoichiometric
amounts of SeO2, unselective, low product yield (30-70%), needs
inert atmosphere, toxic, involves an exhaustive work-up, large
amount of metal waste produced, occurs only at elevated
temperatures and so on. Hence, the development of
environmentally friendly, operationally simple, mild and efficient
methodology for the synthesis of glyoxals is very desirable and
remains a challenging task for exploration.
two decades ago, Fukuzumi’s group14 have reported a mild
protocol for the reductive dehalogenation of arylacyl bromides
into corresponding acetoarylones. Subsequently, several research
groups were utilized Hantzsch esters15, alkyl amines16,, allyl
stannanes, etc17., as reductive quenchers for arylacyl radicals to
synthesize alkyl aryl ketones under visible-light photocatalyzed
conditions. Based on these reports, we hypothesized that reaction
between arylacyl radicals and molecular oxygen (O2) would
provide aryl glycols under mild and green conditions. Moreover,
we intended to synthesize arylacyl bromides in situ from
acetoarylones; so that aryl glycols perhaps obtained in one-pot
procedure known to minimize time and chemical waste.
In continuation of our studies on the visible-light photoredox
catalysis18, herein we describe a novel one-pot method for the
synthesis of aryl/heteroaryl glyoxals from acetoarylones under
visible-light (blue LEDs: h = 42515 nm) photocatalyzed
conditions, cf. Scheme 1. In addition, we account an application
of this methodology for the oxidation of monoamine oxidase-B
inhibitors19, i.e., 1-(4-((4-fluorobenzyl)oxy)phenyl)ethanone and
1-(3-((4-chlorobenzyl)oxy)phenyl)ethanone into their glyoxal
derivatives. Indeed, all reactions proceeded under ambient
conditions and pure products were obtained readily by
recrystallization or filtration through short pad silica gel column
chromatography. To the best of our knowledge, oxidation of
aryl/heteroaryl methyl ketones to aryl/heteroaryl glyoxals via
visible-light initiated protocol has not yet been reported in the
literature.
Since the seminal works from the research groups of
MacMillan7, Stephenson8, Yoon9 and others10, visible light (400-
700 nm) induced organic synthesis11 has appeared as a promising
strategy to access various building blocks, natural products and
drugs12. Significant energy efficiency, simple reaction setup,
environmental friendly, mild reaction conditions and good to
excellent yields are some important characteristics of this class of

2
Tetrahedron Letters
Results and Discussion
Dioxane dibromide (DDB)20, a solid brominating agent, has
been successfully used for the selective mono-bromination of
polycyclic-aromatic
hydrocarbons21,
alkylarylketones22,
coumarins23, etc24., at room temperature. Thus, we preferred
DDB for the conversion of acetoarylones into arylacyl bromides.
Nevertheless, initially, an optimization study was carried out with
a model reaction between acetophenone (AA1, 1.0 equiv.,) and
DDB (1.1 equiv.,) to examine whether it gives only the -
monobrominated product, i.e., phenacyl bromide. Several
Scheme 1. A selenium dioxide-free one-pot oxidation of
aryl/heteroaryl methyl ketones to their corresponding glyoxals
under visible-light photocatalysed conditions reported in this
work.
Table 1. Selected results of screening the optimal conditions for the photocatalytic one-pot oxidation of acetophenone (AA1) to phenyl glyxoal
(AG1) at ambient conditionsa
Entry
Solvent
b
Photo-redox
catalyst
Reductive
Time
(h)
36
Yield
(%) c
17d
26
14e
<10f
0g,h
quencher
1
2
3
4
5
6
7
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
[Ru(bpy)3]Cl2
Et3N
[Ru(bpy)3]Cl2
[Ru(bpy)3]Cl2
[Ru(bpy)3]Cl2
[Ru(bpy)3]Cl2
[Ru(bpy)3]Cl2
[Ru(bpy)3]Cl2
Et3N
36
Et3N
36
Et3N
36
Et3N
36
sodium ascorbate
Diisopropylethyla
mine
18
91
20
16
8
9
CH3CN
CH3CN
[Ru(bpy)3]Cl2
[Ru(bpy)3]Cl2
Triphenylamine
ammonium
20
20
11
38
oxalate
10
11
12
13
14
15
16
17
18
19
20
21
glyme
[Ru(bpy)3]Cl2
[Ru(bpy)3]Cl2
[Ru(bpy)3]Cl2
[fac-Ir(ppy)3]
Eosin Y
sodium ascorbate
sodium ascorbate
sodium ascorbate
sodium ascorbate
sodium ascorbate
sodium ascorbate
sodium ascorbate
sodium ascorbate
sodium ascorbate
sodium ascorbate
sodium ascorbate
sodium ascorbate
18
18
18
18
18
8
22
DMF
88
C2H4Cl2
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
24
47
36
[Ru(bpy)3]Cl2
[Ru(bpy)3]Cl2
[Ru(bpy)3]Cl2
Nil
92i
90j
94k
0h
93i,l
<5i,m
<5i,n
8
8
8
[Ru(bpy)3]Cl2
[Ru(bpy)3]Cl2
[Ru(bpy)3]Cl2
7
8
8
a
Unless stated otherwise all reactions were performed in a Schlenk tube with 1.1 mmol of DDB, 1.0 mmol of AA1, 3.0 mmol of
reductive quencher and 1mol% photo-redox catalyst in dry solvent under air with the irradiation of a 5W blue LEDs (h = 42515 nm).
b Solvents were rigorously purified following the methods described in reference [25]
c Isolated yields.
d a household fluorescent lamp used.
e 5W green LEDs used.
f 15W ambient lamp used.
g no irradiation source used.
h phenacyl bromide isolated in quantitative yield.
i 2% [Ru(bpy)3]Cl2 used.
j 3% [Ru(bpy)3]Cl2 used.
k 5% [Ru(bpy)3]Cl2 used.
l Reaction performed under O2 atmosphere using a balloon
m Reaction performed under Ar atmosphere
n Reaction performed under N2 atmosphere

3
solvents including hexane, toluene, acetonitrile, dichloromethane,
carbon tetrachloride, dioxane, N,N-dimethyl formamide, ethanol
and water were investigated. The best results were achieved using
aprotic polar solvents like acetonitrile, N,N-dimethyl formamide
and dioxane. When acetonitrile was used as a reaction medium,
TLC analysis suggested the formation of single product. The
structure of the isolated product (yield 96%) was confirmed by
NMR and elemental analysis (Electronic Supporting Information,
ESI) in comparison with known compound from literature data.20
Results suggest that the phenacyl bromide has been formed
exclusively.
With the optimized reaction conditions in hand, we further
explored the scope of this protocol (Scheme 1) for synthesis of
electronically diverse aryl glyoxals (AG1-AG21) from
corresponding acetoarylones. To our delight, the electronic
properties of the acetoarylones had little effect on this
transformation (Table 2). For examples, acetoarylones substituted
by electron-donating (CH3, OCH3, and OC2H5) and electron-
withdrawing substituents (F, Cl, NO2 and CF3) were effectively
oxidized into the desired aryl glyoxals in good yields, cf. Table 2.
More importantly, electron rich furan (AA18), thiophene (AA19)
and polycyclic aromatic hydrocarbons (AA15-AA17) as well as
3-acetyl-4-methylpyridine (AA21) were well tolerated, leading to
desire glyoxals in good yield (Table 2 and ESI). Moreover, to
access the feasibility of applying this method on a preparative
scale, we carried out the oxidation of AA4 on a 100 mmol scale.
As expected, the reaction proceeded smoothly; similar to the case
in a smaller scale, and the expected 4-methoxyphenyl glyxoal
was obtained in 91% yield.
Next, the reaction conditions for one-pot synthesis (Scheme 1)
of aryl glyoxals from acetoarylones under photoredox catalyzed
conditions were optimized. Irradiation of solution of
acetophenone (AA1, 1.0 equiv.) in acetonitrile containing DDB
(1.1 equiv.), [Ru(bpy)3]Cl2 (1.0 mol%) and triethylamine (3.0
equiv.) under an open air atmosphere (without air bubbling) at
room temperature with a household fluorescent lamp for 36 h
afforded the desired phenylglyoxal (AG1) in 17% yield (Table 1,
Entry 1). Encouraged by this initial result, a series of trial
experiments were performed to optimize the influences of
radiation source, solvents, catalyst and its quantity, reductive
quencher and atmosphere on the reaction shown in Scheme 1.
Interestingly, the yield of AG1 enhanced to 26% when the
reaction was performed with 5W blue light-emitting diodes
(LEDs, h = 42515 nm, Table 1 and Entry 2). In contrast, the
reaction did not proceed satisfactorily when the reaction was
irradiated with either 5W green LEDs or ambient lights (Table 1,
Entries 3 and 4) or in the absence of light irradiation (Table 1 and
Entry 5). We then went on to study the effect of reductive
quencher on the reaction (Scheme 1): a better yield of AG1 was
obtained when sodium ascorbate was used (Table 1 and Entry 6).
Nevertheless, other quenchers including diisopropylethylamine,
triphenylamine and oxalates afforded moderate yield of AG1
(Table 1 and Entries 7-9). Afterwards, the influence of solvents
(Table 1 and Entries 10-12) such as glyme, dimethylformamide,
dichloroethane, heptane and diethyl ether on the formation of
AG1 was investigated. The investigation revealed that DMF or
CH3CN was the most effective medium to promote the reaction
with 88-91% yield (Table 1, Entries 6 and 11). A maximum yield
of AG1 in DMF or CH3CN was may be due to the greater
solubility of both the catalyst and reductive quencher in that
medium. Nevertheless, CH3CN was used throughout the
synthesis due to easy handling and removal from the product. We
then studied the effect of other photocatalysts such as [fac-
Ir(ppy)3] and eosin Y, but none of them gave better results than
[Ru(bpy)3]Cl2. The influence of quantity of catalyst on the
product yield was also investigated. An increase in the catalyst
amount from 1 mol% to 2 mol%, the reaction time was obviously
shortened (18 h to 8 h) with 92% yield of AG1 (Table 1 and
Entry 15). Further increase in catalyst amount had profound
effect on neither in reaction time nor in yield of the desired
product (Table 1, Entries 16 and 17). However, no product was
observed in the absence of catalyst [Ru(bpy)3]Cl2 (Table 1 and
Entry 18). Subsequently, we investigated the influence of
atmosphere on the reaction. Under open-air atmosphere or O2
(balloon), an excellent yield of AG1 was obtained (Table 1 and
Entry 19), whereas in oxygen-free conditions product was
detected in negligible quantities (Table 1, Entries 20 and 21).
Thus, the combinations of 1.1 equiv. of DDB, 2 mol% of
[Ru(bpy)3]Cl2, 3 equiv. of sodium ascorbate and 5W blue LEDs
in CH3CN at room temperature for 8 h are the optimal conditions
for one-pot synthesis of aryl glyoxals from acetoarylones as
described in Scheme 1.
Table 2. Visible-light-mediated one-pot oxidation of
acetoarylones into aryl glyoxals under optimized reaction
conditions.a
Entry
1
Ar
Substrate Product Yield
(%)b
91
AA2
AG2
2
89
AA3
AG3
3
4
91
86
AA4
AA5
AG4
AG5
5
6
7
91
88
90
AA6
AA7
AA8
AG6
AG7
AG8
8
84
85
87
AA9
AG9
9
AA10
AA11
AG10
AG11
10

4
Tetrahedron Letters
11
12
92
AA12
AA13
AG12
AG13
87
Scheme
2.
Oxidation
of
1-(4-((4-
1-(3-((4-
fluorobenzyl)oxy)phenyl)ethanone
(top)
and
chlorobenzyl)oxy)phenyl)ethanone (bottom) to their glyoxal
derivatives.
13
86
AA14
AG14
Conclusions
In summary, we have developed a novel and operationally
simple method for the direct oxidation of acetoarylones including
14
15
89
83
AA15
AA16
AG15
AG16
monoamine
fluorobenzyl)oxy)phenyl)ethanone
oxidase-B inhibitors
such as
and
1-(4-((4-
1-(3-((4-
chlorobenzyl)oxy)phenyl)ethanone into corresponding glyoxals
using dioxane dibromide, blue LEDs, ascorbate, 2 mol%
[Ru(bpy)3]Cl2, and O2 (air) as valuable reagents. A broad
tolerance of aromatic rings, one-pot consolidated procedure,
large-scale synthesis, easy isolation of the products and good
yield are principal advantages of this procedure. Further work is
progress in our laboratory to investigate the mechanism and
scope of this protocol for the oxidation of dialkylketones and
other derivatives.
16
86
AA17
AG17
17
18
19
89
91
87
AA18
AA19
AA20
AG18
AG19
AG20
Acknowledgments
P.N. gratefully acknowledges the financial support of the
Department of Science & Technology (DST-SERB), India, through
start-up research grant for young scientists [SB/FT/CS-
117/2013]. Manjeet and N. K. thank the University Grant
Commission (UGC), New Delhi for junior research fellowships
(JRF).
Supplementary Data
20
83
AA21
AG21
General synthetic procedure, experimental characterization
data and copies of NMR spectra for selected products prepared
by the method described here. This material is available free of
charge via the Internet.
a
Reaction conditions: 1.1 mmol of DDB, 1.0 mmol of AA, 3.0 mmol of
sodium ascorbate, 2mol% of [Ru(bpy)3]Cl2, dry CH3CN and 5W blue LEDs
(h = 42515 nm) irradiation under open air atmosphere. b Isolated yield.
References and notes
1.
2.
A. Akbari, Synlett., 2012, 23, 951.
Finally, to show the applicability of the developed one-pot
process, we aimed to oxidize monoamine oxidase-B inhibitors19
such as 1-(4-((4-fluorobenzyl)oxy)phenyl)ethanone and 1-(3-((4-
chlorobenzyl)oxy)phenyl)ethanone (Scheme 2) under standard
conditions described in Table 1. In both cases, the reactions were
complete within 8 h affording the desired products in 86% and
82% yields. Thus, a mild and efficient one-pot method described
here offers a domain for synthesis of highly functionalized- as
well as electron rich glyoxals (Table 2, Scheme 2 and ESI) that
cannot be accessed via traditional SeO2 mediated reactions
known to simultaneously oxidize allylic, benzylic, -CH3, and so
on.20
(a) Q. Gao, S. Liu, X. Wu, J. Zhang, and A. Wu, Org. Lett., 2015,
17, 2960; (b) D. Kumar, M. Pilania, V. Arun, and B. Mishra,
Synlett., 2014, 25, 1137; (c) S. Khodabakhshi and B. Karami, New
J. Chem., 2014, 38, 3586; (d) B. Eftekhari-Sis, M. Zirak, and A.
Akbari, Chem. Rev., 2013, 113, 2958.
3.
4.
5.
6.
K. Takahashi, J. Biol. Chem., 1968, 243, 6171.
H. von Pechmann, Chem. Ber., 1887, 20, 2904.
H. A. Riley, and A. R. Gray, Org. Synth., 1943, 2, 509.
Although HX-DMSO mixture has been shown to oxidize
acetoarylones into aryl glyoxals, but that method suffer with poor
yield due to product decomposition while separation through
distillation of product from DMSO. See: M. B. Floyd, M. T. Du,
P. F. Fabio, L. A. Jacob, and B. D. Johnson, J. Org. Chem., 1985,
50, 5022.
7.
8.
(a) A. Nicewicz, and D. W. C. MacMillan, Science, 2008, 322, 77;
(b) P. V. Pham, D. A. Nagib, and D. W. C. MacMillan, Angew.
Chem. Int. Ed., 2011, 50, 6119; (c) Z. Zou, D. T. Ahneman, L.
Chu, J. A. Terrett, A. G. Doyle, and D. W. C. MacMillan, Science,
2014, 345, 437; (d) J. D. Cuthbertson, and D. W. C. MacMillan,
Nature, 2015, 519, 74.
(a) C. Dai, J. M. R. Narayanam, and C. R. J. Stephenson, Nat.
Chem., 2011, 3, 140; (b) J. J. Douglas, H. Albright, M. J. Sevrin,
K. P. Cole and C. R. J. Stephenson, Angew. Chem. Int. Ed., 2015,

5
54, 14898; (c) T. M. Monos, G. Magallanes, L. J. Sebren, and C.
R. J. Stephenson, J. Photochem. Photobiol. A, 2016, 328, 240.
(a) T. P. Yoon, M. A Ischay, and J. Du, Nat. Chem., 2010, 2, 527;
(b) T. P. Yoon, ACS Catal., 2013, 3, 895; (c) D. M. Schultz, and
T. P. Yoon, Science, 2014, 343, 6174;
9.
10. (a) H. Jiang, X. An, K. Tong, T. Zheng, Y. Zhang and S. Yu,
Angew. Chem., Int. Ed., 2015, 54, 1; (b) Y. Liang and D. E.
Bergbreiter, Catal. Sci. Technol., 2016, 6, 215; (c) M. Jiang, H.
Yang, and H. Fu, Org. Lett., 2016, 18, 1968; (d) Q-Y. Lin, Y. Ran,
X-H. Xu, and F-L. Qing, Org. Lett., 2016, 18, 2419; (e) X. Yu and
S. M. Cohen, J. Am. Chem. Soc., 2016, 138, 12320; (f) D. Yang,
B. Huang, W. Wei, J. Li, G. Lin, Y. Liu, J. Ding, P. Suna and H.
Wang, Green Chem., 2016, 18, 5630.
11. (a) D. R. Heitz, J. C. Tellis, and G. A. Molander, J. Am. Chem.
Soc., 2016, 138, 12715; (b) X. Yu and S. M. Cohen, J. Am. Chem.
Soc., 2016, 138, 12320; (c) A. Sagadevan, P-C. Lyu and K. C.
Hwang, Green Chem., 2016, 18, 4526; (d) I. Ghosh and B. Konig,
Angew. Chem. Int. Ed., 2016, 55, 7676.
12. (a) J. J. Douglas, M. J. Sevrin, C. R. J Stephenson, Org. Proc. Res.
Dev., 2016, 20, 1134; (b) N. A. Romero and D. A. Nicewicz,
Chem. Rev., 2016, 116, 10075.
13. (a) M. H. Shaw, J. Twilton, and D. W. C. MacMillan, J. Org.
Chem., 2016, 81, 6898; (b) A. Juris, V. Balzani, F. Barigelletti, S.
Campagna, P. Belser, and A von Zelewsky, Coord. Chem. Rev.,
1988, 84, 85.
14. S. Fukuzumi, S. Mochizuki, and T. Tanaka, J. Phys. Chem., 1990,
94, 722.
15. (a) J. M. R. Narayanam, J. W. Tucker, and C. R. J. Stephenson, J.
Am. Chem. Soc., 2009, 131, 8756; (b) J. H. Lee and S-I. Mho, J.
Org. Chem., 2015, 80, 3309; (c) J. Luo, X. Zhang, and J. Zhang,
ACS Catal., 2015, 5, 2250.
16. P. Natarajan, Manjeet, and N. Kumar, Advances in Chemistry
Research; Vol. 34, ed. J. C. Taylor, Nova Science Publishers,
U.S.A., 2016, ch-9.
17. (a) C. K. Prier, D. A. Rankic, and D. W. C. MacMillan, Chem.
Rev., 2013, 113, 5322; (b) D. Staveness, I. Bosque, and C. R. J.
Stephenson, Acc. Chem. Res., 2016, 49, 2295.
18. (a) P. Natarajan, A. Bala, S. K. Mehta, and K. K. Bhasin,
Tetrahedron,2016, 72, 2521; (b) P. Natarajan, N. Kumar, and M.
Sharma, Org. Chem. Front., 2016, 3, 1265.
19. Z-M. Wang, X-M. Li, W. Xu, F. Li, J. Wang, L-Y. Kong, and X-
B. Wang, Med. Chem. Commun., 2015, 6, 2146.
20. L. F. Fieser and M. Fieser, Reagents for Organic Synthesis, Vol;
1, Wiley, New York, NY,1967, p.334.
21. G. M. Kosolapoff, J. Am. Chem. Soc., 1953, 75, 3596.
22. S. J. Pasaribu, and L. R. Williams, Aust. J. Chem., 1973, 26, 1327.
23. S. K. Chaudhuri, S. Roy, and S. Bhar, Beilstein. J. Org. Chem.,
2012, 8, 323.
24. (a) D. C. Schlegel, C. D. Tipton, K. L. Rinehart Jr, J. Org. Chem.,
1970, 35, 849; (b) S. K. Chaudhuri, S. Roy, M. Saha, and S. Bhar,
Synth. Commun., 2007, 37, 579.
25. W. L. F. Armarego, C. L. L. Chai, Purification of laboratory
chemicals, 6th ed.; Butterworth-Heinemann, Oxford, 2009.

6
Tetrahedron Letters
 Novel visible-light induced synthesis of 6-
arylphenanthridines reported
 In situ produced aryl diazonium salts have
been employed as a source of aryl radicals
 1% [Ru(bpy)3]Cl2 used as a photo-redox
catalyst.
 Complete conversion with up to 94% yield
was noticed.